To better understand the mechanisms of pulsed laser-assisted synthesis of metal nitride, a numerical model was proposed to simulate the process of laser nitriding of aluminum. The model incorporated various multiphysical processes in the laser nitriding process, including heating, melting and vaporization of aluminum, formation of plasma plume, shielding of laser energy, ionization of nitrogen gas, and the transport of nitrogen in the chemically active state N* (N atoms and N+ ions) inside the aluminum. The simulated results are in good agreement with the existing experimental results in terms of laser intensity, laser impulse, N+ lifetime in plume, and nitrogen diffusion depth in aluminum. The model can well simulate the laser shielding process by plume and the nitriding process of aluminum. Characteristics of the plume expansion, plasma formation, nitrogen ionization, and diffusion were investigated systematically by the developed model. Investigations on the effects of key operating conditions show that the impact of laser wavelength is negligible, while the full-width at half-maximum (FWHM), nitrogen gas pressure, and laser intensity have a significant impact on the laser nitriding process of aluminum. The larger FWHM and larger laser intensity yield a layer with a higher N* concentration and greater thickness. The higher nitrogen gas pressure leads to an increase in N* concentration at the same position.

Microbubbles have been widely used in many research fields due to their outstanding physicochemical properties and unique structural characteristics, especially as ultrasonic contrast agents and drug delivery carriers. However, the stability of conventional microbubbles is generally poor, which limits the development of their applications. Loading nanoparticle to microbubbles has great potential in enhancing the stability of microbubbles. This paper reports for the first time the feasibility of one-step preparation of nanoparticle-loaded microbubbles by coaxial electrohydrodynamic atomization. Bovine serum albumin (BSA) was used as the model material of the bubble shell layer to study the effect of the loading of nanoparticles on the stability of microbubbles. The results show that the concentration of nanoparticles has a significant impact on the stability of microbubbles, and loading an appropriate amount of nanoparticles is helpful in improving the stability of microbubbles. The results also show that nanoparticle-loaded microbubbles with a size distribution in the range of 120–200 μm can be prepared under optimal conditions.